The present invention is directed to aqueous ink-jet ink compositions having reduced aerosol resulting in less satellite spotting as well as a method for printing images with an ink-jet ink having reduced aerosol and satellite spotting.
In recent years, computer printer technology has evolved to a point where very high-resolution images can be transferred to various types of media, including paper. One particular type of printing (referred to generally as ink-jet printing) involves the placement of small drops of fluid ink onto a media surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. Within this general technique, the specific method by which the ink-jet ink is deposited onto the printing surface varies from system to system, and can include continuous ink deposit and drop-on-demand ink deposit.
Essentially, continuous printing systems function as a stream of ink droplets are ejected and directed by the printer nozzle. The ink droplets are directed with the assistance of an electrostatic charging device in close proximity to the nozzle. In a continuous printing system, if the ink is not directed onto the print media, it is recycled for later use. Similarly, in drop-on demand printing systems, the ink-jet inks are typically based upon water and glycols. With drop-on-demand systems, ink droplets are propelled from a nozzle by heat or by a pressure wave. Additionally, all of the ink droplets formed are used to form printed images.
Low cost and high quality of output, combined with relatively noise free operation, have made ink-jet printing a popular alternative to other computer related forms of printing. However, even though great improvement in ink-jet printing has been made, demand for higher quality ink-jet printing systems has arisen. Presently, regardless of the method employed to eject ink from an ink-jet printer, a common problem experienced in ink-jet printing is the disintegration of an ejected ink droplet such that certain portions of the original ink droplet do not reach the intended position on the print media. More specifically, problems arise related to the generally known fact that an ink droplet ejected by an ink-jet printer forms a head portion and a tail portion upon ejection. Often, the tail portion of an ejected ink droplet will become susceptible to random aerodynamic forces and will fragment into smaller volumes of ink. These small volumes of ink are commonly referred to as break off remnants, and can become misdirected, thereby failing to deposit at the intended location on the print media along with the intact head portion of the ejected ink droplet. Exacerbating the above mentioned misdirection of ink, such break off remnants are often small enough that their trajectory can be further altered by random aerodynamic forces. Break off remnants are known collectively as aerosol and, when misdirected, individual break off remnants of the aerosol form what are commonly referred to as satellite drops, which can form satellite spotting on the print media.
The formation of aerosol and resultant satellite drops are an undesirable occurrence during the ink-jet printing process. This is in part because control over the final position of an ejected ink droplet on the print media is effectively withdrawn from the control of the printer microprocessor and diverted to random aerodynamic forces, thereby reducing the over all sharpness and definition of the image or character being printed. Additionally, aerosol negatively affects print quality by diminishing the amount of ink directed to create a particular image, area fill, or other pattern.
Not all break off remnants that can create satellite spotting are misdirected. Typically, in order for a break off remnant to be misdirected, it generally must be small enough to be materially affected by the random aerodynamic forces to which it is exposed, and the fragmentation of the tail portion creating the break off remnant will generally have occurred sufficiently far from the print medium destination to provide an opportunity for those forces to alter the flight path of the satellite drop. In practice, the size of the break off remnants and the time at which break off occurs are largely affected by the interaction between three factors 1) inertial forces at work or xe2x80x9cdragxe2x80x9d, 2) the viscosity of the ink, and 3) the surface tension of the ink.
Accordingly, it is recognized that a substantial need exists to reduce or eliminate the formation of aerosol effects and satellite drops (and thus, satellite spotting on print media) in ink-jet printing through the manipulation of the three factors mentioned above. Such an endeavor is made difficult by the fact that often one of these three factors may not be optimized without adversely affecting another. In particular, fluid friction or drag in ink-jet inks have typically been thought to be inversely proportionate to viscosity and surface tension. Additionally, any composition or method for accomplishing these goals should provide a solution wherein the ink-jet ink composition is sufficiently stable in an aqueous solution so as to be practical in a commercial application.
The present invention is drawn to an aqueous based ink-jet ink composition and a method for printing images exhibiting reduced satellite spotting (in size and amount), by employing effective amounts of certain high molecular weight polysaccharides. Specifically, an aqueous inkjet ink composition exhibiting a reduction in aerosol formation during printing is disclosed, comprising an ink vehicle; an effective amount of at least one ink colorant; and from 5 to 200 ppm of a high molecular weight polysaccharide. Similarly, a method of printing an image on a substrate with reduced satellite spotting around the image on the substrate comprises the steps of formulating an ink-jet ink composition described above, followed by jetting the ink-jet ink composition from an ink-jet pen, wherein aerosol formation of the ink-jet ink composition is substantially reduced resulting in a substantial reduction is satellite spotting around the image. Further, a system for producing ink-jet ink images having reduced satellite spotting comprises an ink-jet ink composition comprising an effective amount of an ink vehicle, an effective amount of at least one ink colorant, and from 5 to 200 ppm by weight of a high molecular weight polysaccharide; and an ink-jet pen containing said ink-jet ink composition, said ink-jet pen configured to jet said ink-jet ink composition onto a substrate. With the composition, method, or system described herein, the polysaccharide can have an average molecular weight from about 200,000 to 5,000,000, preferably from 1,000,000 to 5,000,000.